The present invention relates in general to the recovery of sulfur from waste gases, and in particular to a new and useful method and arrangement for removing sulfur from sour gases which are produced by cleaning coke oven gases.
In a crude coke oven gas cleaning process, it may be provided that the vapors or sour gases from the cleaning plant, which plant comprises gas strippers as the last stage, contain the entire amount of hydrogen sulfide, the entire amount of ammonia, hydrogen cyanide, a part of the carbon dioxide, and a small proportion of benzene hydrocarbons. This may particularly be the case if ammonia and hydrogen sulfide are stripped from the crude oven gas in a so-called closed cycle ammonia-hydrogen sulfide scrubber. The content worth recovering of these sour gases is only the hydrogen sulfide which is processed to sulfuric acid or sulfur. The proportion of ammonia and hydrocyanic acid is of no interest and according to prior art methods, these substances may be decomposed and burned (see German Pat. No. 1,925,839; German AS No. 1,925,840; German AS No. 2,639,651; German Pat. No. 1,223,818; German Pat. No. 2,537,451; and German Pat. No. 1,926,629).
Methods for recovering sulfur from coke oven gases are known, for example from German Pat. Nos. 1,925,839, 1,926,629 and 2,537,451, and they provide combustion with fuel gas, or air enriched in both stages with hydrocarbons, or oxygen enriched air, or pure oxygen, all at ambient temperature, thus with a temperature of 5.degree. to 25.degree. C. Particular equipment is needed for producing oxygen or oxygen-enriched air. Therefore, economy calls for the use of air. Further, in the prior art, the two stages, namely the disintegration and the oxidation stages, operate at considerably different temperatures, the difference being at least 200.degree. C., i.e. the oxidation stage operates at temperatures which are by about 200.degree. C. higher than those of the disintegration stage. Heat economy would require a smaller difference. Also, the prior art oxidation stage is followed by cooling the gases in one or more stages, for example in a waste heat boiler and a cooler, and the cooling is conducted up to a separation of aqueous condensates from the gases. This is done because the water vapor produced during the combustion of fuel gas or hydrocarbons burdens the process gas and dilutes the sulfur compounds. Condensation of the water vapor does result in a concentration of sulfur compounds. The gas, however, must be cooled down to a point of condensation and then again brought up to about 200.degree. to 400.degree. C., the working temperature of the catalytic Claus reaction. This is an additional heat supply unfavorably affecting the total thermal balance. In addition, prior art processes frequently require a processing of the residual Claus gases including a hydrogenation and subsequent scrubbing to prevent formation of sulfur dioxide-containing waste gases, and their escape into the atmosphere or into the crude coke oven gas.